LONDON, Aug 3 (Reuters) - Athletics took centre stage atLondon 2012 on Friday when home favourite Jessica Ennis thrilleda raucous crowd in the heptathlon, while U.S. swimmers hoggedthe limelight in the pool.

Britain, dominant in track cycling in Beijing four yearsago, took its second and third gold medals in the velodrome,while New Zealand picked up two rowing golds in the space of 40minutes.

Michael Phelps, the most decorated Olympian of all time, wonhis 21st medal by claiming the men's 100 metres butterfly.

Katie Ledecky, 15, took the women's 800m freestyle title andanother teenage U.S. swimmer, 17-year-old Missy Franklin,grabbed her third gold medal of the Games in the 200mbackstroke, breaking the world record in the process.

Older competitors also had their day.

Sergei Martynov, a 44-year-old Belarussian, used a13-year-old gun and bullets from the Soviet era to win the men's50 metres prone rifle with a world record score.

In archery, Oh Jin-hyek, 30, won South Korea's first men'sOlympic individual archery gold medal after beating TakaharuFurukawa of Japan in the final at Lord's cricket ground.

"I was not as good at sports in my 20's, but now I've turned30 and I want to keep doing sports for a long time," said Oh,who had tried to break into the mighty national Olympic team fora decade.

TRACK THRILLS

With the start of the athletics, the jewel in the Olympiccrown, excitement began to build towards Jamaican Usain Bolt'sdefence of his 100 metres title on Sunday and his 200 crown fourdays later.

Ennis, the London Games poster girl whose every move wasgreeted with deafening roars at the 80,000-capacity stadium, washoping to add to Britain's rising medal tally after setting aworld best time for a heptathlete in the 100 metres hurdles.

Britain's former world champion followed up with a solidhigh jump but Lithuiania's Austra Skuyte set an Olympic recordfor the shot put in the heptathlon to take the overall lead.

A short but heavy morning downpour could not dampen spiritsat the main arena, where loud recorded music from Coldplay toQueen blared out in a cross between an athletics meet and a popconcert.

World champion Vivian Cheruiyot of Kenya was beginning herbid for a distance double in a much-anticipated 10,000 metresfinal where Ethiopian Olympic champion Tirunesh Dibaba, who hasthe fastest time of the year, is expected to be her main rival.

Cheruiyot also has her eye on the 5,000 next week as sheattempts to replicate her double gold from last year's worldchampionships.

PENDLETON RECOVERS

At Wimbledon, Roger Federer of Switzerland remained oncourse to repeat his heroics in the Grand Slam in July, beatingArgentina's Juan Martin del Potro in a marathon 19-17 third andfinal set for a place in the final.

Federer will now face local hope Andy Murray who rode a waveof British euphoria to beat Serbia's world number two NovakDjokovic 7-5 7-5 and set up a repeat of last month's Wimbledonfinal against the Swiss maestro.

New Zealand struck gold twice on the water, with MaheDrysdale taking the men's single sculls and men's pair EricMurray and Hamish Bond cruising to victory in comprehensivefashion.

Germany powered to gold in the men's quad sculls, finallygetting their revenge on the young Croatian crew who had beatenthem all season.

But another German rower, Nadja Drygalla, who has alreadyfinished competing at the Games, voluntarily left the Olympicvillage following reports that her boyfriend was a far-rightextremist.

In cycling, the British men beat Australia in the teampursuit, setting a world record, and Victoria Pendleton won thewomen's keirin, a day after being disqualified with JessicaVarnish in the team sprint.

Britain's men took cycling track team sprint gold onThursday, but the taste of victory was soured when German-bornrider Philip Hindes admitted to falling over on his bike onpurpose in the heats to avoid being disqualified.

"I did it on purpose to get a restart ... it was all plannedreally," he told reporters, prompting shock among British mediaand leading to calls for a change in the rules.

It also raised uncomfortable questions about gamesmanship atthe Olympics, after eight badminton players were thrown out fordeliberately losing matches to manipulate the draw, breaking thespirit, but not the rules of their sport.

British cycling officials later said Hindes' comments werelost in translation and the International Olympic Committee hasno plans to investigate the incident "at present".

China's head badminton coach Li Yongbo took a swipe at thesport's federation and said enough punishment had been dealt tothe eight expelled players and their teams for their part in thematch-throwing scandal.

Li was ordered to make a public apology by China's nationaldelegation this week and said he was to blame for the negativetactics of his world champion pair Yu Yang and Wang Xiaoli, whowere among those kicked out along with two Indonesians and fourfrom South Korea.